在 iOS 中用 Swift 绘制/编辑 CVPixelBuffer 的正确方法

Question

是否有一种标准的高性能方法可以快速编辑/绘制 CVImageBuffer/CVPixelBuffer？

我在网上找到的所有视频编辑演示都将绘图（矩形或文本）覆盖在屏幕上，并且不直接编辑 CVPixelBuffer。

更新我尝试使用 CGContext 但保存的视频不显示上下文绘图

private var adapter: AVAssetWriterInputPixelBufferAdaptor?

extension TrainViewController: CameraFeedManagerDelegate {
    
    func didOutput(sampleBuffer: CMSampleBuffer) {

        let time = CMTime(seconds: timestamp - _time, preferredTimescale: CMTimeScale(600))
        let pixelBuffer: CVPixelBuffer? = CMSampleBufferGetImageBuffer(sampleBuffer)

        guard let context = CGContext(data: CVPixelBufferGetBaseAddress(pixelBuffer),
                                  width: width,
                                  height: height,
                                  bitsPerComponent: 8,
                                  bytesPerRow: CVPixelBufferGetBytesPerRow(pixelBuffer),
                                  space: colorSpace,
                                  bitmapInfo: alphaInfo.rawValue)
        else {
          return nil
        }

        context.setFillColor(red: 1, green: 0, blue: 0, alpha: 1.0)
        context.fillEllipse(in: CGRect(x: 0, y: 0, width: width, height: height))
        context.flush()

        adapter?.append(pixelBuffer, withPresentationTime: time)


    }
}

Answer 1

您需要CVPixelBufferLockBaseAddress(pixelBuffer, 0)在创建位图之前CGContext以及CVPixelBufferUnlockBaseAddress(pixelBuffer, 0)完成绘制到上下文之后调用。

不锁定像素缓冲区，CVPixelBufferGetBaseAddress()返回 NULL。这会导致您CGContext分配新的内存来绘制，该内存随后被丢弃。

还要仔细检查您的色彩空间。很容易混淆您的组件。

例如

guard
    CVPixelBufferLockBaseAddress(pixelBuffer) == kCVReturnSuccess,
    let context = CGContext(data: CVPixelBufferGetBaseAddress(pixelBuffer),
                            width: width,
                            height: height,
                            bitsPerComponent: 8,
                            bytesPerRow: CVPixelBufferGetBytesPerRow(pixelBuffer),
                            space: colorSpace,
                            bitmapInfo: alphaInfo.rawValue)
else {
    return nil
}

context.setFillColor(red: 1, green: 0, blue: 0, alpha: 1.0)
context.fillEllipse(in: CGRect(x: 0, y: 0, width: width, height: height))

CVPixelBufferUnlockBaseAddress(pixelBuffer)

adapter?.append(pixelBuffer, withPresentationTime: time)